Multi-level ballast circuit including an isolation transformer for series circuit connection with a fluorescent lamp



y 1967 F. P. EPPERT 3,333,150

MULTI-LEVEL BALLAST CIRCUIT INCLUDING AN ISOLATION TRANSFORMER FORSERIES CIRCUIT CONNECTION WITH A FLUORESCENT LAMP Filed Sept. 30, 1964 2Sheets-Sheet 1 INVENTOR. flan/W0? PIE gnarl:

BULL? United States Patent 3,333,150 MULTILEVEL BALLAST CIRCUITINCLUDING AN ISOLATION TRANSFORMER FOR SERIES CIRCUIT CONNECTION WITH AFLUORES- CENT LAP/l1 Franklin P. Eppert, Danville, Ill., assignor toGeneral Electric Company, a corporation of New York Filed Sept. 30,1964, Ser. No. 400,447 7 Claims. (Cl. 315-97) This invention relates toan improved ballast circuit for use with fluorescent lamps. Morespecifically, it relates to a ballast circuit arrangement which providestwo-level operation of fluorescent lamps.

In present commercial practice when using two-level ballasts withparallel connected fluorescent lamps it is necessary to include in thelamp circuits a separate pair of switching contacts for each ballast. Ifthe separate switching contacts are not provided it has been found thatunbalanced lamp operating levels result, with one lamp burning brighterthan the others. Also, with a single switch in series with severalparallel connected lamps it is impossible to uniformly control the lampcurrents at lower levels.

It is an object of this invention to provide an improved ballast circuituseful for operating fluorescent lamps at two levels of output.

It is an object of this invention to provide a ballast circuitarrangement wherein the impedances of several ballasts, each of which isconnected in series with one of several parallel connected fluorescentlamps, can be changed by the operation of a single pair of switchingcontacts.

It is a further object of this invention to provide a ballast circuitarrangement wherein two levels of operation of fluorescent lamps areprovided with uniform output of the lamps at each level.

These objects are accomplished in accordance with this invention, in oneform thereof, by including one Winding of an isolation transformer inseries with each fluorescent lamp. A switch is connected in series withthe other windings of the isolation transformers, which are connected inparallel if more than one is used. The windings may be open-circuited orshort-circuited by the switch. When the contacts are operated to shortcircuit the windings, the impedances of the windings in series with thelamps are reduced, thereby raising the output levels of the lamps.

Other objects and further details of that which is believed to be novelwill be clear from the following description and claims taken with theaccompanying drawings wherein:

FIGURE 1 is a schematic circuit diagram of a ballast circuit for severalparallel connected fluorescent lamps including the improved circuitry ofthis invention.

FIGURE 2 is a schematic circuit diagram of a ballast circuit for asingle fluorescent lamp including the improved circuitry of thisinvention.

FIGURE 1 shows a first embodiment of the subject invention in whichthree fluorescent lamsp L L and L are connected in parallel. Atransformer T is provided with a primary winding P which is energized byan AC power source having terminals 1 and 2. A capacitor 3 is connectedin parallel with the primary winding P for power factor correction.Transformer T has four secondary windings, S 8 S and S These secondarywindings are used to heat the cathodes in lamps L L and L Secondarywinding S is used to heat one of the cathodes in each of the threelamps, while windings 8 S and S are used to heat the other cathodes inlamps L L and L respectively. One cathode of each of the three lamps isconnected to terminal 1 of the AC power supply by lead 4.

3,333,150 Patented July 25, 1967 Isolation transformers T T and T areprovided with primary windings P P and P respectively, all of which areconnected to terminal 2 of the AC power supply by leads 5. The otherterminals of the primary windings P P and P are connected to one of theterminals of ballast reactors R R and R respectively. The otherterminals of the reactors R R and R are connected to the secondterminals of the lamps L L and L respectively, by leads 6, 7, and 8,respectively. Each of the isolation transformers T T and T is providedwith a secondary winding S S and S respectively. Corresponding terminalsof the three secondary windings are connected to each other and theparallel connected secondary windings are also connected in parallelwith contacts of an on-01f switch 9.

With the switch 9 in the off position, as shown, the reactances of theprimaries P P and P of transformers T T and T are large. Therefore, thelamps L L and L operate at a low level as the power supplied to eachlamp is limited by the reactances of a transformer primary winding and aballast reactor.

With the switch 9 in the on position, the reactances of the primarywindings P P and P are reduced according to well-known transformerprinciples, and therefore increased power is supplied to the lamps L Land L Thus, with switch 9 in the on position the lamps are operated at ahigher output level than with the switch 9 in the oil? position. Withoutthe physical interruption of the three parallel circuits, each includingin series a ballast reactor, a transformer primary winding and a lamp,it is possible to alter the impedance of each of the three parallelcircuits by closing or opening the contacts of switch 9.

The turns ratios of the isolation transformer windings are chosen suchthat the current in the secondary winding and the voltage developedacross it are compatible with the voltage and current ratings of theswitch 9.

With the control circuit shown in FIGURE 1, the operating level of eachof the three lamps is controlled by a single switch 9', but the failureof an individual isolation transformer, reactor, or lamp, afiects onlyits circuit, the remainder of the lamps continue to operate in a normalmanner with the switch 9 continuing to control their output level.

It can easily be seen that a greater number of parallel lamp circuitscould be added to this ballast circuit, with the operating level of allof the lamps being controlled by a single switch 9. The cathodes ofthese additional lamps could be energized by transformer T or a separatetransformer could be provided for each additional group of three lamps.In either case, the secondary windings of the isolation transformerswhose primaries are each connected in series with one of the lamps wouldall be connected in parallel, whereby the switch 9 would control theoperating level of all of the lamps.

Similarly, two or more lamps connected in series could replace each ofthe lamps L L and L to increase the number of lamps controlled by thesingle switch 9. If two or more lamps were connected in series,additional ballast reactance would also be required, and could beobtained by connecting an additional reactor in series with eachisolation transformer primary.

By reference to FIGURE 2, it will be seen that a single fluorescent lampL is energized by a ballast transformer T5. This transformer has aprimary P which is connected by lines 10 and 11 to the terminals of anAC power supply. The transformer T has a main magnetic core 12, and alsoa bridging core portion 13 which provides a high leakage reactancebetween the primary winding P and a secondary winding S It will beunderstood, of course, that various other arrangements for providingleakage flux paths or shunts between the primary winding P and thesecondary winding S may be employed. Depending upon the design of theparticular ballast transformer, either air leakage paths, insertedshun-ts, or shunts integrally formed on the magnetic core 12 may beemployed.

Transformer T is also provided with two additional secondary windings Sand S which are used to heat the cathodes of lamp L Winding S isconnected to one of the cathodes of lamp L; by leads 14 and 15, whilewinding S is connected to the other cathode of tube L; by leads 16 and17. The cathode of lamp L, which is connected to secondary winding S isalso connected to one side of the primary winding P and therefore toterminal 11 of the AC power supplied by lead 18. One terminal of thesecondary winding S is connected to a terminal of the primary winding Pand to terminal 9 of the AC power supply by lead 19. An isolationtransformer T is provided with a primary winding R; which is connectedin series with the secondary winding S and the lamp L, by leads 20 and21, respectively. The contacts of an on-oil switch 22 are connected to asecond-ary winding S on transformer T; by leads 23 and 24. The operationof this ballast circuit is similar to that shown in FIGURE 1. With theswitch 22 in the off position, as shown, the reactance of the primarywinding P of the transformer T is large, and therefore the lamp Loperates at a low level. The power supplied to the lamp L being limitedby the reactances of the transformer windings S and P With the switch 22in the on position, the reactance of a primary winding P is reducedaccording to well-known transformer principles, and therefore increasedpower flows to the lamp L with the output of lamp L thereby beingincreased.

While particular embodiments of the invention have been shown, otherembodiments of the invention, such as the use of two or more isolationtransformers in series with each lamp to give multilevel lamp operation,will be apparent to those skilled in the art, and it is intended tocover .by the appended claims all embodiments falling within the scopethereof.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. A ballast circuit for varying the output level of a hot cathodefluorescent lamp energized by an alternating current source, saidcircuit comprising:

(a) a first transformer having a primary winding and a plurality ofsecondary windings, (b) a capacitor connected to said transformer forcorrecting the power factor of said circuit, (c) means for connectingsaid secondary windings to heat the cathodes of the lamp,

(d) an isolation transformer having a primary and a secondary winding,

(e) a reactor for limiting current to the lamp during operation,

(f) means for connecting said isolation transformer primary winding andsaid current limiting reactor in series between the lamp and the source,

(g) a bilaterally conducting switch connected to said secondary windingwhereby with said switch closed said secondary winding is shortcircuited during successive half cycles of applied voltage and said lampoperates at a higher level, and with said switch open, said lampoperates at a lower level.

2. A ballast circuit for varying the output level of a fluorescent lampenergized by an alternating current source, said circuit comprising:

(a) a transformer having a first winding, and a high reactance secondarywinding,

(b) means for connecting said first winding to the alternating currentsource,

(-c) an isolation transformer having a primary and a secondary winding,

(d) means for connecting said high reactance secondbetween the lamp andthe source,

(e) bilaterally conducting switch means connected to I said secondarywinding whereby with said switch means in a closed condition saidsecondary winding is short circuited during successive half cycles ofapplied voltage and said lamp operates at a higher level, and with saidswitch means in an open condition, said lamp operates at a lower level.

3. A ballast circuit for varying the output level of a hot cathodefluorescent lamp energized by an alternating current source, saidcircuit comprising:

(a) a transformer having a first winding, a high reactance secondarywinding, and additional secondary windings,

(b) means for connecting said first winding to the alternating currentsource,

(c) means for connecting each of said additional secondary windings toheat one of the cathodes of the lamp,

(d) an isolation transformer having a primary and a secondary winding,

(e) means for connecting said high reactance secondary winding and saidprimary winding in series between the lamp and the source,

(f) a switch connected to said secondary winding whereby with saidswitch closed said secondary winding is short circuited duringsuccessive half cycles of applied voltage and said lamp operates at ahigher level, and with said switch open, said lamp operates .at a lowerlevel.

4. Arballast circuit useful for operating fluorescent lamps at twooutput levels from an alternating current source, said circuitcomprising:

'(a) isolation transformers, each having a primary and a secondarywinding,

(b) means for connecting each of said primary windings in series withone of the lamps,

(c) means for connecting all of said second-ary windings in parallelwith each other,

(d) switch means connected in parallel with said secondary windings,whereby with said switch means in a closed condition said secondarywindings are short-circuited and said lamps operate at a higher level,and with said switch means in an open condition, said lamps operate at alower level.

5. A ballast circuit useful for operating fluorescent lamps at twooutput levels from an alternating current source, said circuitcomprising:

(a) ballast reactors, and means for connecting each ballast reactor inseries with one of the lamps,

(b) isolation transformers, each having a primary and a secondarywinding,

(c) means for connecting each of said primary windings in series withone of the lamps, f

(d) means for connecting all of said secondary Win-dings connected inparallel with each other,

(e) switch means connected in parallel with said secondary windings,whereby with said switch means in a closed condition said secondarywindings are short-circuited and said'lamps operate at .a higher level,and with said switch means in an open condition, said lamps operate at,alower level.

6. A bal last'circuit useful for operating rhot cathode fluorescentlamps at two output levels from an alternating current source, saidcircuit comprising:

(a) a transformer having a first winding and several secondary windings,p

(-b) means for connecting said first Winding to the alternating currentsource,

(c) means for connecting one of said secondary windings to heat one ofthe cathodes in each of the lamps,

(d) means for connecting each of said other secondary 5 windings to heatthe other cathode in one of the lamps,

(e) isolation transformers, each having a primary and a secondarywinding,

(f) means for connecting each of said primary windings in series withone of the lamps,

(-g) means for connecting all of said secondary windings in parallelwith each other,

(h) a switch connected in parallel with said secondary windings, wherebywith said switch closed said secondary windings are short-circuited andsaid lamps operate at a higher level, and with said switch open, saidlamps operate at a lower level.

7. A ballast circuit useful for operating hot cathode fluorescent lampsat two output levels from an alternating current source, said circuitcomprising:

(e) ballast reactors, and means for connecting each ballast reactor withone of the lamps,

(f) isolation transformers, each having a primary and a secondarywinding,

(-g) means for connecting each of said primary windings in series withone of the lamps,

(h) means for connecting all of said secondary windings in parallel witheach other,

(i) a switch connected in parallel with said secondary windings, wherebywith said switch closed said secondary windings are short-circuited andsaid lamps operate at a higher level, and with said switch open, saidlamps operate at a lower level.

References Cited UNITED STATES PATENTS 1,926,423 9/1933 Barclay 315-2552,665,394 1/1954 Arvidsson et al. 315-97 2,774,917 12/1956 Passmore315-97 2,961,579 1-1/1960 Roney et al. 315-170 3,070,743 12/1962 Harper323-86 X 3,182,249 5/1965 Pahlavan 323-50 X JAMES W. LAWRENCE, PrimaryExaminer.

C. R. CAMPBELL, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3,333,150 July 25, 1967 Franklin P. Eppert It is hereby certified thaterror appears in the above numbered patent requiring correction and thatthe said Letters Patent should read as corrected below Column 6, line 2,after "reactor" insert in series Signed and sealed this 24th day ofSeptember 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

1. A BALLAST CIRCUIT FOR VARYING THE OUTPUT LEVEL OF A HOT CATHODEFLUORESCENT LAMP ENERGIZED BY AN ALTERNATING CURRENT SOURCE, SAIDCIRCUIT COMPRISING: (A) A FIRST TRANSFORMER HAVING A PRIMARY WINDING ANDA PLURALITY OF SECONDARY WINDINGS, (B) A CAPACITOR CONNECTED TO SAIDTRANSFORMER FOR CORRECTING THE POWER FACTOR OF SAID CIRCUIT, (C) MEANSFOR CONNECTING SAID SECONDARY WINDINGS TO HEAT THE CATHODES OF THE LAMP,(D) AN ISOLATION TRANSFORMER HAVING A PRIMARY AND A SECONDARY WINDING,(E) A REACTOR FOR LIMITING CURRENT TO THE LAMP DURING OPERATION, (F)MEANS FOR CONNECTING SAID ISOLATION TRANSFORMER PRIMARY WINDING AND SAIDCURRENT LIMITING REACTOR IN SERIES BETWEEN THE LAMP AND THE SOURCE,